The present invention relates generally to cellulosic fiber composites using protein hydrolysates, and to the method of using protein hydrolysates in the manufacture of agricultural and other cellulosic fiber composites.
Currently, petroleum based binders such as polymeric isocyanates, phenolic and other formaldehyde-based resins, including phenol formaldehyde, phenol resorcinol formaldehyde, and urea formaldehyde, are employed in the manufacture of cellulosic fiber composites such as agfiber board and oriented strand board. However, these binders exhibit several disadvantages such as formaldehyde emissions, high temperature requirements to enable the binders to set, difficulty in handling of resins, and high materials and production costs. It would be desirable to reduce the amount of phenolic and isocyanate resin employed in the production of cellulosic fiber composites.
U.S. Pat. No. 4,944,823 (""823) describes a method for bonding wood surfaces together by heating and pressing using a dry binder formulation constituting a thorough mixture of an isocyanate and a carbohydrate such as a sugar or starch in the manufacture of composite wood products. The sugar or starch replaces a quantity of the isocyanate which would normally have been used, thereby reducing the total quantity of isocyanate. However, the binder described by the ""823 patent does not include a source of protein nor protein hydrolysate.
Natural legume-based resins have been employed with cellulosic material in the preparation of rigid, pressure-formed biocomposites (U.S. Pat. Nos. 5,593,625 and 5,635,123). These embodiments employ close to equal amounts of legume-based resin and fiberous cellulosic solids (40-56% resin solids) in the production of fiber-reinforced, protein-based discrete high moisture-content particles having a moisture content of about 55-75% by weight. By assuring that the moisture content remains above 59% by weight, the relatively high amount of legume-based resin fully impregnates the particles such that a new composite material is prepared rather than a material that is produced by gluing fiberous cellulosic solids together by an adhesive. The particles can be combined with a secondary thermosetting binder to form the biocomposite materials. As a result, preparation of such biocomposites requires an additional drying step to reduce the moisture content to less than about 20% by weight prior to pressing.
It would be desirable to produce finished cellulosic fiber composites through a method which employs materials having a relatively low moisture content and which does not require an additional drying stage or step. Therefore, there remains a need for a new fiber-adhesive, resin binder system for use in the manufacture of agricultural and other cellulosic fiber composites, which reduces the amount of phenolic and/or isocyanate resin needed.
The present invention meets this need by providing cellulosic fiber composites, methods for preparing cellulosic fiber composites, and finished cellulosic fiber composite articles. The cellulosic fiber composites comprise a cellulosic material and a resin binder comprising protein hydrolysates and a synthetic resin, wherein the synthetic resin is phenolic resin, isocyanate resin, or combinations thereof. The composites contain an effective amount of resin binder so as to bind together the cellulosic material.
In accordance with the present invention, a resin binder is prepared by first hydrolyzing protein to produce protein hydrolysates. The protein can be animal protein, vegetable protein, or combinations thereof. More particularly, the vegetable protein can be soy isolate, soy flour, or a blend thereof.
The resultant protein hydrolysates can be mixed with a synthetic resin to produce a resin binder. The synthetic resin of the resin binder can be phenolic resin, isocyanate resin, or combinations thereof. The amount of resin binder included in the composite can be between about 2% and about 15% of the dry weight of the cellulosic material. Optionally, the amount of resin binder included in the composite can be between about 4% and about 8%, between about 4% and about 6%, or between about 4% and about 5% of the dry weight of the cellulosic material.
After application of the resin binder, the average moisture content of the cellulosic material can be between about 8% and about 35% by weight. If the synthetic resin is phenolic resin, the weight ratio of protein hydrolysates to phenolic resin making up the resin binder can be between about 10:90 and about 90:10. Optionally, this weight ratio can be between about 10:90 and about 75:25. Alternatively, this weight ratio can be between about 25:75 and about 75:25, or between about 25:75 and about 50:50.
If the synthetic resin is isocyanate resin, the weight ratio of protein hydrolysates to isocyanate resin making up the resin binder can be between about 10:90 and about 90:10. Optionally, this weight ratio can be between about 10:90 and about 75:25. Alternatively, this weight ratio can be between about 25:75 and about 75:25, or between about 25:75 and about 50:50.
Optionally, the synthetic resin may also be a combination of phenolic resin and isocyanate resin. The weight ratio of the isocyanate resin to the total of the protein hydrolysates and the phenolic resin making up the resin binder can be between about 25:75 and about 75:25.
Optionally, the synthetic resin can further comprise paraformaldehyde. The weight ratio of the paraformaldehyde to the total of the protein hydrolysates and the synthetic resin making up the resin binder can be between about 2:48 and about 15:35 based on 50% resin solids.
Optionally, the synthetic resin can further comprise a high methylol content phenol formaldehyde pre-polymer. The weight ratio of the high methylol content phenol formaldehyde pre-polymer to the total of the protein hydrolysates and the synthetic resin making up the resin binder can be between about 10:90 and about 90:10. Optionally, this weight ratio can be between about 25:75 and about 75:25.
Optionally, the cellulosic fiber composite can further comprise a silicone, silane, and combination thereof. The silicone, silane, or combination thereof can be applied as a coating to the composite, or it can be added to the resin binder to improve such properties as high temperature strength, water resistance, and decreased swelling caused by absorption of water.
The present invention is also directed to methods for preparing cellulosic fiber composites. These methods comprise: mixing a protein hydrolysate with a synthetic resin to produce a resin binder. The synthetic resin can be phenolic resin, isocyanate resin, or combinations thereof. The protein hydrolysates are prepared by hydrolyzing a source of protein with sodium carbonate. The synthetic resin can further comprise paraformaldehyde or high methylol content phenol formaldehyde pre-polymer. These methods further comprise: mixing the resin binder with cellulosic material, wherein the amount of resin binder added can be between about 2% and about 15% of the dry weight of the cellulosic material, to form a cellulosic material/resin binder blend; felting the cellulosic material/resin binder blend to form a low moisture-content mat; and pressing the low moisture-content mat at an elevated temperature and pressure, producing a cellulosic fiber composite. The moisture content of the composite can later be adjusted to a predetermined amount. A silicone, silane, or combination thereof may alternatively be applied to the cellulosic fiber composite as a coating, or added as part of the resin binder.
In addition, the present invention is also directed to finished cellulosic fiber composite articles, as well as methods for preparing finished cellulosic fiber composite articles. Alternatively, a laminate overlay can be applied to these finished articles.
Accordingly, it is an object of the present invention to provide cellulosic fiber composites comprising cellulosic material and a resin binder in which the resin binder contains a reduced amount of petrochemicals, and to provide methods for preparing such composites.